This invention relates to precision valving, precision pumping and precision dispensing utilizing a squeezing action for compressive action upon the side walls of a tube; both apparatus and method, certain of which have utility both alone and in various combinations. A compensator valve disclosed herein has wide application for interruption of flow independent of its particular usefulness in the disclosed valve/pump and/or precision dispensing systems.
The disclosed new precision positive displacement valve/pump using the compensator valve and precision dispensing mechanisms and methods are useful in dispensing work fluids of wide variety and are particularly useful for deposition on a substrate and "dumps" for potting, etc. They are also very useful in the individual low volume high precision depositions application of work fluids at a high repetitive rate of separate depositions.
Precision flow control and precision dispensing is affected by characteristics of the flowable work material being dispensed. Among the flowable work material characteristics which affect shut off or control of flow and/or repeatable, practical precision using positive displacement type pumping and dispensing are the characteristics of (i) viscosity, (ii) chemical stability, (iii) the amount and character of the particulates in the work material, (iv) material thermal properties, and (v) the air and/or other gas in the work material both inherent and entrained. Among the wide variety of materials which may be pumped are acrylics, anaerobics, braising pastes, conductive epoxys, cyanoacrylates, epoxys, lubricants, potting compounds, sealants, silicones, solder creams, and solder masks.
Constriction of a squeezable tube for flow control is a well known art. By squeezing a flexible tube shut, (sides meet) flow of a work material internally of the tube is interrupted. Conversely, the flow of the work material is permitted when the squeezing thereof is relieved due to the resilience of the tube itself coupled with a head or other source pressure on the flowable work material.
The act of squeezing a resilient tube shut at some point intermediate the ends of the tube inherently displaces the flowable work material in the tube in the area being squeezed together. Simply put, the flowable work material must go somewhere (assuming the work material is substantially non compressible). When the tube is squeezed shut, either ballooning the tube and/or forcing the material back toward source and/or as is the more usual, when the constriction functions as an outlet shut off, it causes a displacement discharge through the outlet.
The usual means of causing shut off of flow is by causing a movable member to have squeeze action against a tube located intermediate it and a fixed anvil or group of movable members move toward both the tube and each other. The moving members action is generally reciprocal and generally at right angles to the axis of the tube, although roller squeezing and cam action squeezing are also well known and here the usual attack/retreat angle of the movement of these members is not at right angles to the tube axis.
There are applications for the shut off of flow where displacement because of squeezing of the tube during shut off is not desirable. This occurs where, for example, control of the flow is desired in that range of infinitessimal flow to that amount inherently imposed by the displacement surge during squeezing action of shut off. Also surge or pressure changes on the flow because of shut off may be unwanted in some particular systems application(s).
A shut off type valve for squeezable tubes which does not have a displacement surge affect on outlet flow from the tube is particularly advantageous in precision dispensing of minute adjustable quantities of work material on a substrate, as in dispensing tiny dots of work material on very tiny electronic/electrical circuit board or chip substrates. Also such a non-displacement type of shut off is desirable where another displacement means (a separate displacement member usually having much more surface area that the shut off member) is associated with the tube for displacement pumping. Thus the quantity of material being displaced is but under the control of the displacement means, rather than the combination of the displacement means and the shut off member. By use of a nondisplacement type shut off, when the displacement means is adjustable or controllable to adjustably control volume being displaced, the range of adjustment is inherently increased when contrasted with a displacement type shut off, since the threshold amount: of displacement caused by shut off is eliminated. Operational control of the displacement pump may also be simplified, since control is essentially associated with one part of the pump. This is advantageous particularly in systems where programmable aspects of the displaced volumes is discrete such as in computer or programmable logic controller control of the displacement means of the pump.
In those applications requiring precision dispensing which are associated with manufacturing processes, the practical requirements of any dispensing system are low cost, reproducible precision at quite high speed, sufficient throughput for the application needs, and if it can be provided at reasonable low cost, versatility and adjustability, versus dedicated single usage. It is helpful in most manufacturing environments that the dispensing apparatus and method be adapted to be controlled by and combined with a programmable controller which will coordinate the various parts of the apparatus and in some environments may simultaneously coordinate the workpiece area for movement of work pieces relative to the dispensing outlet(s).
Squeezable tube pumps find commercial appeal in dispensing of multiple source work liquids that are delivered to a mixer prior to delivery to a dispensing outlet, and are very appealing in dispensing many single component or pre-mixed multiple component work fluids. They also enjoy usefulness in single or multiple outlet dispensing and may also find usefulness downstream of a multicomponent mixer intermediate the outlet of the mixer and the dispensing head.
Dispensing apparatus using squeeze tube pumps are particularly useful in Z towers and/or in XYZ movable head and/or movable work area apparatus type devices. Further, where the character and nature of the work material being pumped to the outlet does not afford easy clean up, they may be used with disposable tubes which may be replaced after a work shift or other discrete segment of use. They are also well adapted for use with cartridge types of work materials where a multi-component type work material is pre-packaged in a cartridge for later dispensing. For example some modern precision dispensing systems use a cartridge of work material which prior to use is kept frozen or at a low temperature to deliberately slow chemical action. The cartridge is then thawed at the manufacturing site just prior to dispensing and then dispensed in the interval prior to the work material becoming unmanageable for pumping.
It will be appreciated that the work piece areas beneath (or above) the dispensing outlet(s) may be characterized as locating a temporarily fixed work piece, or a work piece which is subject to rotational movement or is continuously or intermittently movable in some combination of linear or rotational movements and/or a part of an automatic work piece transfer system. It will also be appreciated that there exist manufacturing environments where the precision deposition required is of a nature where the work material after deposition essentially should contain no gas. In some high precision electronic/electrical applications, the electronic/electrical components may require very close tolerances of final characteristics of the deposited work material. These work materials when dispensed in normal circumstances would have entrained gases therewithin which can change the desired electrical characteristics of the deposited bead, dot or encapsulation type work material on/in the workpiece. Where substantially gas free ultra-high precision deposition is required, many of these work materials may be degassed by vacuum techniques prior to dispensing and then further degassed for dispensing in a vacuum chamber so as to completely or almost completely degas such material.
Another important aspect of precision dispensing is the characteristics and needs of the particular application envisioned, i.e. what type of deposition is needed with respect to the workpiece. For example, dispensed dots in sizes ranging from almost microscopic up to those of sizes in the vicinity of 1/4 inch diameter (and larger) are used in manufacturing. Additionally some applications may require a continuous or discontinuous bead in straight line, rectilinear or triangular configuration, or arcuate or circular configuration, and/or a relatively large volumetric deposition in a single dispensing shot such as may be used in encapsulation or potting type applications.
The highest precision automatic dispensing system with greatest versatility involves positive displacement and any of a variety of pumping hardware and related hardware options, a personal computer, a programming system and a control system. The programming (software or handwired board or combination) involves a PATTERN program, a CONTROL program and a SYSTEM program. The purpose of these three programs is to afford user adjustability and preferably involves a screen readable approach.
The purpose of the PATTERN program is to create and store a program for execution of the dispensing of a preselected particular work material upon a preselected particular type of work piece part with the particular dispensing hardware and related hardware involved in the system. Ideally the PATTERN program will include multiple capabilities, such as plotting a program, imaging the program (and/or printing) on a screen, the ability to clear and start over, the ability to retrieve a prior developed program or pattern, the ability to edit a pattern, the ability to store and/or delete a pattern, the ability to name or rename a pattern, the capability of editing a pattern and ability to enter and/or exit the PATTERN program. The very sophisticated PATTERN program will provide for movement of the dispensing head in X/Y/Z planes in coordination with positive displacement pumping and will afford programming of directional movements of the dispensing head, velocity of movement, line movement, circular movement, arcuate movement, rectilinear movement, pause capability, speed capability and a host of coordinating capabilities regarding relationships with other components of a larger system (employing for example work material heaters/vacuum degassers/work material source conditioning/and work piece movers. Importantly, it will provide the programs for the positive displacement pumping of work material in specific relative locational aspects of the work piece and the dispensing outlet(s). The PATTERN program in its sophisticated form will also include communication capability with other devices. It also somewhat overlaps with the CONTROL program.
The major purpose of a CONTROL program is to execute the PATTERN program that is created (either newly created or previously created and stored). Ideally, in addition to mere execution it will have some powerful other capabilities. A sophisticated control program will allow adjustability of speeds of execution, adjustability of locations of execution, easy selection of any previously created or newly created program, a "jogging" of the output head to operator selected positions (by tracing, etc. around a work piece and/or templet and/or plotting board or drawing) and recording the position for future repeating and a host of other set up procedures. For example, dimension(s) of work area space for movement of heads may be changed, number of work units to be addressed may changed, the tolerance of error may be changed, the flow time delay may be changed and the "size of the fill" stop may be changed. Also the status of various components of the hardware maybe ascertained for on/off or sequencing of movements of other portions cf the system (such as movement or non-movement to preselected positions for valves, the X position of the dispensing head, the Y position of the dispensing head, the Z position of the dispensing head, the dispensing level of the source, the velocity of movement of the head and/or work piece in various planes or axis and percent of velocity of movement relationships. These may involve coordination of various types with movements and relationships with themselves or other operations and events. A sophisticated CONTROL system will also afford a manual and/or automatic purging to the dispensing head and/or source of work material and/or tubing/piping/valves/needles/mixers, etc. The purging may be necessitated to address such problems as clogging by work material and/or for gas bubbles and may be used in conjunction with or without a vacuum degassing system.
The purpose of the SYSTEM program is for determining the logic by which the entire dispensing system operates. It preferably has decision making capability, and may be simple or very sophisticated such that it may interrelate to or with other computers and/or systems. Once this logic is established, the CONTROL program will work based upon the logic in the SYSTEM program, i.e. it is a fundamental to the CONTROL program. The CONTROL program will await for certain input signals and then act upon those input signals. It may await certain commands from a computer and may download commands to a computer. A powerful SYSTEM program affords intercommunication not only with components of a large system but additionally with the operator/user. A sophisticated SYSTEM program ideally, once determined and established, will not be changed, however capability of change of the logic structure is desirable.
The highest precision dispensing apparatus and systems having versatility will include hardware capable of moving an outlet(s) in any of 3 or more axis; are useful with a variety of work materials; are adaptable for dispensing single or multiple slots to a work piece(s) with controlled volumes in any preselected pattern or amount; are characterized as being operable to coact with a variety of work piece movers, work material controls, and ambient or contrived environmental situations (vacuum or pressurized); and include hardware and components which will respond with high precision to software capable of afore generally described PATTERN, CONTROL and SYSTEM programs.
A squeezable outlet valve per se is shown in the co-pending application entitled Method and Apparatus for Precision Pumpinq, Ratioing and Dispensing of Work Fluid(s) having U.S. patent application Ser. No. 07/118,330 filed Nov. 6, 1987 and assigned to the same assignee. In that apparatus the squeezable tube is located intermediate the output end of the mixer and the dispensing outlet but in essence operates as a shut off valve with the upstream movement of the roller providing some suck back characteristics. The roller shut off valve is essentially on/off and is operated in conjunction with a piston/cylinder pump. This pump is driven by a precision stepper motor which in turn is computer controlled.
The nature of the aforementioned apparatus of the co-pending application is such that the positive displacement mechanism (piston/cylinder) is relatively large in size and is cumbersome in nature. The apparatus requires a relatively large base, frame, and support mechanism and inlet/outlet valving remotely located from the work piece area and the outlet(s). Also, the pumping is quite remote from the roller on/off squeeze tube dispensing valves. The system shown also requires on/off valve(s) associated with the positive displacement pumping in addition to the roller shutoff squeeze tube valve. While the aforementioned apparatus taught in the copending application teaches extremely fine precision control of single and multiple work fluids with multiple outlets for dispensing, and the coordination control of the positive displacement pumping with other moving parts of the apparatus, it is relatively bulky and expensive. The co-pending disclosed piston/cylinder positive displacement pump(s) mechanism can be advanced or retreated in exceedingly small increments or steps. Because the co-pending disclosed ball screw mechanism operates through a gear reducer and has inherent mechanical advantages itself, it will produce relatively large torques to dispense a relatively large mass of flowable work material with very good control capabilities on volume dispensed. Also that apparatus is also well adapted for fairly large volumetric dispensing quantities with an almost infinite adjustment of the volume.
In addition to cost, positive displacement piston/cylinder pumps are not well adapted for use with all pumpable materials, including many of those hard to pump types such as those with high particulate content. They are also not well adapted for. disposable type cartridge packed work materials or fast setting or other material(s) which cause clean up to become onerous. A movable piston/cylinder type pump of the aforediscussed co-pending high precision type is not well adapted to be "hung" on a Z tower or disposed on the end of a Z arm of an XYZ mechanism. Further the copending squeeze tube shut off valve does displace material upon shut off which defines a lower threshold limit of volume of material to be dispensed.
Positive displacement pump dispensing apparatus where a squeezable tube is used in the system is shown in an issued patent in the prior art. In addition to the aforementioned co-pending application, a positive displacement system using a squeezable tube in the system is shown in U.S. Pat. No. 3,932,055, entitled PNEUMATICALLY CONTROLLED LIQUID TRANSFER SYSTEM which issued Jan. 13, 1976. This system shows a pair of squeezable tubes; one tube is located intermediate the source and a piston/cylinder and the other intermediate the piston/cylinder and the outlet. They are so arranged that the mechanism requires the piston to engage the work fluid in the cylinder chamber apart from the squeezable tubes. (The inlet and outlet to the system both being squeezable tubes which are acted on by a valving mechanism which alternately shuts and opens the inlet and outlet in coordination with the piston/cylinder.) Here, because of the use of the piston/cylinder for displacement pumping, the system has the problem of not being usable for many hard to pump work materials and also is relatively expensive and cumbersome. It is not well adapted to be disposed on the end of a Z arm of an XYZ device. In essence this system shows both inlet and outlet valves for the pump using squeeze tubes, but the positive dispensing means does not work directly on the squeezable tube. The positive displacement of work material in this system is an inadvertent aspect of "shut off" valving
Replaceable squeeze tubes are also shown in U.S. Pat. No. 4,450,981 issuing May 29, 1984 and entitled PRECISION MATERIAL FILLING SYSTEM. However this system is not a positive displacement system since work material flow is essentially caused by relief of the squeezing action, thereby allowing pressure in the source of the work material to cause flow (except for unintended displacement caused by shut off pinching).
A squeezable tube valve/pump mechanism is known to be marketed commercially in the United States under the name of SCM/Dispensit of Indianapolis, Ind. In this mechanism, the movable inlet, outlet and displacement member all act directly upon the flexible tube. The anvil opposite the displacement member is manually adjustable to provide adjustability to the volume displaced by squeezing movement of the displacement member. In the SCM/Dispensit apparatus, the movable inlet, outlet and dispensing tube impinging members are each actuated by air cylinders in a timed sequence. The movable tube impinging outlet member (on/off) necessarily surges or displaces work material during shut off. The air cylinder actuator for the movable tube engaging dispensing member causes essentially on/off actuation. The construction appears to be such that a complex movement profile of the dispensing member alone or in conjunction with other tube en gaging members, is inherently difficult. The 3 air cylinders cannot give lightweight extremely versatile control of the dispensing member at high speed.
The invention herein overcomes several of the noted prior art problems. In the instant invention, there is disclosed a new method and apparatus for shut off of flow of a flowable work material in a squeezable tube without causing a displacement surge because of the pinching action of the tube engaging shut off member.
In broadest concept, a compensator is incorporated which moves toward and away from the tube in opposite direction to the movements of the shut off member. The compensator has a size of tube engagement area substantially larger than the shut off member and the length of its corresponding opposite direction of movement is less than that of the shut off member. The relative size and stroke lengths are calculated to produce no displacement surge during shut off. In effect the compensator prevents a displacement of work material at the outlet of the tube because it is increasing the volume in the tube intermediate the shut off member and the outlet by the same amount that the shut off member is decreasing the volume as it pinches off.
The compensator member is made adjustable in connection with its length of stroke and its starting position. The starting position may be adjustably located such that it is possible to have a portion of its stroke of movement occur after the shut off member has closed the tube. By causing the compensator to continue movement away from constriction after the pinching, it causes a back pressure to be created. This back pressure is created adjacent the shut off movable member and creates a suck back of work material downstream from the shut off member. Because this portion of the stroke of the compensator member after the shut off is adjustable, it may be adjusted for materials of different physical and chemical characteristics. This adjustability of suck back is important in some applications where versatility is important. Also it is particularly advantageous for fine turning of a computer controlled dispensing pump. An operator, during set up, may adjust this one manual adjustment to account for small system tolerance variables and thereby does not require the operator "going into" and changing the software of the system (where computer control of the dispensor member is employed).
Also a major feature of the invention disclosed herein is a programmable movement of the dispensing member against the tube to provide pumping by positive displacement squeezing. Importantly, the movement of the dispensing member toward and away from the tube may have a complex movement profile as preselected by programing. It may advance/retreat/stop in any of an almost infinite variety of combinations as desired and may be controlled and coordinated with the inlet and outlet members movement. The incremental subdivision of movement are minute and may be in the range of .001 to .00001 inches or smaller. The coordination with the use of the disclosed PATTERN, CONTROL and SYSTEM programs is also adapted to extend to movement of the dispensing outlets in a single or multiple axis and/or with various work piece area movers and/or with other dispensing needs such as work material source control, heaters and degassing apparatus. It is well adapted for use in a wide variety of automatic or so called robotic assembly operations.
Also, the invention includes hardware such that the programmable actuator or mover for the dispensing member is capable of being of relatively light weight so that it may be used on the end of a Z tower or on an XYZ movable head without sacrifice of desired precision. The actuator/mover shown and described is preferably a small stepper motor mounted directly on the valve/pump frame which in turn drives a cam. Other means could be employed such as a servo mechanism with an encoder instead of a stepper motor and various means of translation of the output of the stepper or servo could be employed for engaging the dispenser member (pinion/rack or ball/screw or metal band/roller, etc.). However where relatively light torques are required, the stepper motor directly outputting to a driving cam is compact, lightweight, easy to mount and can provide (with electronic secondary stepping) approximately 50,000 steps per revolution to in turn provide exceedingly fine control of positive displacement dispensing movement.
Further, with the disclosed software, the PATTERN, CONTROL and SYSTEM programming may cause the stepper motor (or other actuator) to be easily coordinated with an equally precisely controlled movement of a dispensing head and/or work piece mover. By programming with the software and using the tiny incremental steps and the fast response movement of the stepper motor, the suck back of the work material at the outlet may be adjustably set for each work material. (Although, as aforementioned, when used with an adjustable compensator, it is preferred that both be used for suckback.) Suck back with the stepper motor is accomplished by moving the dispensing member from constriction toward relief of constriction prior to closing the shut off in the cycling of the tube pump and while the inlet is still closed to afford primary suck back.
Where the system usage requirements are such that the lower end of the range of volume of material being dispensed exceeds the threshold level imposed by the displacement volume caused by a shut off valve without a compensator, suck back can be accomplished solely by adjusting a slight retreat from pinching movement by the dispensing member prior to the shut off being effectuated.
In theory, the displacement pressure surge caused by the shut off member could also be compensated for by programmed movement of the dispensing member in a retreating direction so as to cause a "place" for the shut off pinching displaced material to go to. However, in fast repetitive pumping sequences, and because of movement lag caused by viscosities of work material combined with other complex work material flow affecting parameters, the use of a compensator to the shut off valve is preferred.